Conventionally, there has been proposed a display device with a photosensor that, due to including a photodetection element such as a photodiode inside a pixel, can detect the brightness of external light and pick up an image of an object that has come close to the display. Such a display device with a photosensor is envisioned to be used as a bidirectional communication display device or display device with a touch panel function.
In a conventional display device with a photosensor, when using a semiconductor process to form known constituent elements such as signal lines, scan lines, TFTs (Thin Film Transistor), and pixel electrodes on an active matrix substrate, a photodiode, peripheral circuits, and the like are simultaneously formed on the active matrix substrate (see PTL 1).
A photodiode outputs an electrical signal in accordance with the amount of incident light. Each photodiode is provided with a peripheral circuit that includes a capacitor. For example, each peripheral circuit accumulates a charge in the capacitor in accordance with the level of the electrical signal output by the photodiode, and furthermore generates a photoreception signal whose voltage level varies in accordance with the amount of accumulated charge. Also, each peripheral circuit causes the capacitor to discharge an amount of accumulated charge in accordance with the level of the electrical signal that has been output by the photodiode, and generates a photoreception signal whose voltage level varies in accordance with the amount of charge remaining in the capacitor. Furthermore, each peripheral circuit outputs this photoreception signal to a detection circuit provided outside the display region via a readout line that extends in the vertical direction of the screen.
The detection circuit gathers the signals output by the peripheral circuits, generates image data, performs image processing on the image data, and thereafter outputs the resultant image data to the outside. In this way, the liquid crystal display device disclosed in PTL 1 enables pickup of an image of an object on the observer side of the display screen of the liquid crystal panel.